Projection arrangement for a head-up display (HUD) with P-polarised light portions

ABSTRACT

A projection arrangement for a head-up display, including a composite pane, including an outer pane and an inner pane, which are joined to one another via a thermoplastic intermediate layer, having an upper edge and a lower edge and an HUD region; an electrically conductive coating on the surface of the outer pane or the inner pane facing the intermediate layer or provided within the intermediate layer; and a projector that is aimed at the HUD region; wherein the light of the projector has at least one p-polarised portion and wherein the electrically conductive coating has, in the spectral range from 400 nm to 650 nm, only a single local reflection maximum for p-polarised light, with this maximum in the range from 510 nm to 550 nm.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Stage of PCT/EP2019/052574, filedFeb. 4, 2019, which in turn claims priority to European patentapplication number 18163269.6 filed Mar. 22, 2018. The content of theseapplications are incorporated herein by reference in their entireties.

The invention relates to a projection arrangement for a head-up displayand the use of a composite pane in such a projection arrangement.

Modern automobiles are increasingly equipped with so-called head-updisplays (HUDs). With a projector, typically, in the region of thedashboard, images are projected onto the windshield, reflected there,and perceived by the driver as a virtual image behind the windshield(from his point of view). Thus, important data can be projected into thedrivers field of vision, for example, the current driving speed,navigation or warning messages, which the driver can perceive withouthaving to divert his glance from the road. Head-up displays can thuscontribute significantly to an increase in traffic safety.

With the above described head-up displays, the problem arises that theprojector image is reflected on both surfaces of the windshield. Thus,the driver perceives not only the desired primary image, which is causedby the reflection on the interior-side surface of the windshield(primary reflection). The driver also perceives a slightly offsetsecondary image, usually weaker in intensity, which is caused by thereflection on the exterior-side surface of the windshield (secondaryreflection). The latter is commonly referred to as a ghost image(“ghost”). This problem is commonly resolved in that the reflectingsurfaces are arranged at an angle relative to one another deliberatelyselected such that the primary image and the ghost image aresuperimposed, as a result of which the ghost image is no longerdistractingly noticeable.

Windshields comprise two glass panes that are laminated to one anothervia a thermoplastic film. If the surfaces of the glass panes are to bearranged at an angle as described, it is customary to use athermoplastic film with a non-constant thickness. This is also referredto as a wedge-shaped film or a wedge film. The angle between the twosurfaces of the film is referred to as a wedge angle. The wedge anglecan be constant over the entire film (linear change in thickness) orchange as a function of position (nonlinear change in thickness).Composite glasses with wedge films are known, for example, fromWO2009/071135A1, EP1800855B1, or EP1880243A2.

It is also known to provide windshields with transparent, electricallyconductive coatings. These coatings can act as IR-reflecting coatings toreduce the heating up of the vehicle interior and thus improve thermalcomfort. The coatings can, however, also be used as heatable coatings byconnecting them to a voltage source such that a current flows throughthe coating. Suitable coatings include conductive, metallic layers, forexample, based on silver or aluminium. Since these coatings aresusceptible to corrosion, it is customary to apply them on the surfaceof the outer pane or the inner pane facing the intermediate layer suchthat they have no contact with the atmosphere. Silver-containingtransparent coatings are known, for example, from WO 03/024155, US2007/0082219 A1, US 2007/0020465 A1, WO 2013/104438, or WO 2013/104439.In connection with head-up displays, coated windshields often have theproblem that an additional reflecting boundary surface for the projectorimage is formed by the conductive coating. This results in another andesirable secondary image, which is also referred to as a layer ghostimage or a layer ghost.

The light of the HUD projector is typically substantially s-polariseddue to the better reflection characteristics of the windshield comparedto p-polarisation. However, if the driver wears polarisation-selectivesunglasses that transmit only p-polarised light, he can hardly perceivethe HUD image, or not at all. There is, consequently, a need for HUDprojection arrangements that are compatible with polarisation-selectivesunglasses.

DE 10 2014 220 189 A1 discloses an HUD projection arrangement that isoperated with p-polarised light to generate an HUD image that is alsoperceivable with polarisation-selective sunglasses. Since the angle ofincidence is typically close to Brewster's angle and p-polarised lightis therefore reflected only to a small extent by the glass surfaces, thewindshield has a reflective structure that can reflect p-polarised lightin the direction of the driver. Among other things, a single metalliclayer with a thickness from 5 nm to 9 nm, for example, made of silver oraluminium is proposed as the reflective structure. Although ap-polarised HUD image can be perceived by drivers with and withoutpolarisation-selective sunglasses, it is primarily reflected by themetallic layer, but not significantly by the glass surfaces. This limitsthe intensity of the HUD image.

US 2017/0242247 A1 likewise discloses an HUD projection arrangement thatis operated with p-polarised light, wherein the windshield is providedwith an electrically conductive coating. The electrically conductivecoating has, in the spectral range from 400 nm to 650 nm, a localreflection maximum for p-polarised light, which is in the range from 510nm to 550 nm. The proportion of p-polarised light in the total light ofthe HUD projector is 100%.

The object of the invention is to provide an improved projectionarrangement for a head-up display, wherein the composite pane used isprovided with an electrically conductive coating.

The head-up display should also be readily perceivable even for driverswith polarisation-selective sunglasses and should have high intensity.

The object of the present invention is accomplished according to theinvention by a projection arrangement in accordance with claim 1.Preferred embodiments are disclosed in the dependent claims.

According to the invention, at least partially p-polarised light,preferably a mixture of s- and p-polarised light, is used for generatingthe HUD image. S-polarised light components are efficiently reflected bythe pane surfaces. Since the angle of incidence of about 65° typical forHUD projection arrangements is relatively close to Brewster's angle foran air/glass transition (57.2°, soda lime glass), the p-polarised lightcomponents are, on the other hand, hardly reflected by the panesurfaces. However, the electrically conductive coating according to theinvention is optimized for the reflection of p-polarised light. A driverwith polarisation-selective sunglasses that allow only p-polarised lightto pass can, consequently, perceive the HUD projection that is caused bylight component reflected at the coating. A driver without suchsunglasses perceives an HUD image that is caused by the superimposing ofthe s- and p-polarised light components, as a result of which theoverall intensity is increased. The result is thus an HUD projectionthat can readily be perceived both by drivers withpolarisation-selective sunglasses and by drivers without suchsunglasses. This is the major advantage of the present invention.

The projection arrangement according to the invention for a head-updisplay (HUD) includes at least a composite pane with an electricallyconductive coating and a projector. As is usual with HUDs, the projectorirradiates a region of the windshield where the light is reflected inthe direction of the viewer (driver), generating a virtual image, whichthe viewer perceives, from his point of view, as behind the windshield.The region of the windshield that can be irradiated by the projector isreferred to as the HUD region. The beam direction of the projector cantypically be varied by mirrors, in particular vertically, in order toadapt the projection to the body size of the viewer. The region in whichthe eyes of the viewer must be situated with a given mirror position isreferred to as the “eye box window”. This eye box window can be shiftedvertically by adjustment of the mirrors, with the entire area thusavailable (i.e., the superimposing of all possible eye box windows)referred to as the “eye box”. A viewer situated within the eye box canperceive the virtual image. This, of course, means that the eyes of theviewer must be situated within the eye box, not the entire body.

The technical terms used here from the field of HUDs are generally knownto the person skilled in the art. For a detailed presentation, referenceis made to Alexander Neumann's dissertation “Simulation-BasedMeasurement Technology for Testing Head-Up Displays” at the Institute ofComputer Science at the Technical University of Munich (Munich:University Library of the Technical University of Munich, 2012), inparticular Chapter 2 “The Head-Up Display”.

The composite pane comprises an outer pane and an inner pane that arejoined to one another via a thermoplastic intermediate layer. Thecomposite pane is intended, in a window opening, in particular thewindow opening of a motor vehicle, to separate the interior from theoutside environment. In the context of the invention, the term “innerpane” refers to the pane of the composite pane facing the interior(vehicle interior). The term “outer pane” refers to the pane facing theoutside environment. The composite pane is preferably a motor vehiclewindshield (in particular the windshield of a motor vehicle, forexample, of the passenger car or a truck).

The composite pane has an upper edge and a lower edge as well as twoside edges extending therebetween. “Upper edge” refers to that edge thatis intended to point upward in the installed position. “Lower edge”refers to that edge that is intended to point downward in the installedposition. The upper edge is also often referred to as the “roof edge”;and the lower edge, as the “engine edge”.

The outer pane and the inner pane have in each case an exterior-sidesurface and an interior-side surface and a peripheral side edgeextending therebetween. In the context of the invention, “exterior-sidesurface” refers to that primary surface that is intended, in theinstalled position, to face the outside environment. In the context ofthe invention, “interior-side surface” refers to that primary surfacethat is intended, in the installed position, to face the interior. Theinterior-side surface of the outer pane and the exterior-side surface ofthe inner pane face each other and are joined to one another by thethermoplastic intermediate layer.

The composite pane has an electrically conductive coating, in particulara transparent, electrically conductive coating. The electricallyconductive coating is preferably applied to one of surfaces of the twopanes facing the intermediate layer, i.e., the interior-side surface ofthe outer pane or the exterior-side surface of the inner pane.Alternatively, the electrically conductive coating can also be arrangedwithin the thermoplastic intermediate layer, for example, applied to acarrier film that is arranged between two thermoplastic bonding films.The conductive coating can, for example, be provided as an IR-reflectingsolar protection coating or also as a heatable coating that iselectrically contacted and heats up when current flows through it. Theterm “transparent coating” means a coating that has averagetransmittance in the visible spectral range of at least 70%, preferablyat least 80%, which thus does not substantially restrict vision throughthe pane. Preferably, at least 80% of the pane surface is provided withthe coating according to the invention. In particular, the coating isapplied to the pane surface over its entire surface with the exceptionof a peripheral edge region and, optionally, a local region that areintended to ensure the transmittance of electromagnetic radiationthrough the composite pane as communication windows, sensor windows, orcamera windows, and, consequently, are not provided with the coating.The peripheral uncoated edge region has, for example, a width of up to20 cm. It prevents direct contact of the coating with the surroundingatmosphere such that the coating is protected, inside the compositepane, against corrosion and damage.

The electrically conductive coating is a layer stack or a layersequence, comprising one or a plurality of electrically conductive, inparticular metal-containing layers, wherein each electrically conductivelayer is in each case arranged between two dielectric layers or layersequences. The coating is thus a thin-film stack having n electricallyconductive layers and (n+1) dielectric layers or layer sequences, wheren is a natural number and wherein, on a lower dielectric layer or layersequence, a conductive layer and a dielectric layer or layer sequencefollows alternatingly in each case. Such coatings are known as solarprotection coatings and heatable coatings, wherein the electricallyconductive layers are typically based on silver.

The electrically conductive coating according to the invention isadjusted, in particular through the selection of the materials andthicknesses of the individual layers and the structure of the dielectriclayer sequence, such that in the spectral range from 400 nm to 650 nm,preferably in the spectral range from 400 nm to 750 nm, only a singlelocal reflection maximum for p-polarised light occurs. This reflectionmaximum for p-polarised light is, in particular, in the spectral rangefrom 510 nm to 550 nm. In an advantageous embodiment, this localreflection maximum represents the highest reflection value in thespectral range from 400 nm to 650 nm, i.e., in the spectral range from400 nm to 650 nm, no reflectance for p-polarised light occurs that ishigher than the reflectance of the local maximum.

The inventors have discerned that such an electrically conductivecoating efficiently reflects the p-polarised light components and thecomposite pane also has relatively neutral colouration in transmittanceand reflection. With the coating adjusted according to the invention, itis, in particular, possible to freely select the p-polarised lightcomponent corresponding to the requirements of the individual case, withthe colouration always remaining relatively neutral. Thus, thep-polarised light components can be selected in the individual case, asa function of the projector used, the wavelength of its light, the angleof incidence, and the geometry of the composite pane, such that anadvantageous overall intensity is achieved. The invention is,consequently, flexibly applicable to various HUD systems, whichconstitutes a great advantage.

Decisive for the properties of the projection arrangement is thereflection behaviour of the composite pane, which is essentiallydetermined by the electrically conductive coating. The reflectionspectrum is measured on the composite pane provided with theelectrically conductive coating. Strictly speaking, the reflectionproperties described here for p- or s-polarised light (reflectance,local reflection maximum) thus refer not to the insulated electricallyconductive coating, but to the composite pane with the electricallyconductive coating.

Reflectance describes the proportion of the total incident light that isreflected. It is indicated in % (based on 100% incident light) or as aunitless number from 0 to 1 (normalized to the incident light). Plottedas a function of the wavelength, it forms the reflection spectrum.

The difference between the reflectance for p-polarised light that occursat the local reflexion maximum in the spectral range from 400 nm to 6500nm and the reflectance for p-polarised light minimally occurring in thespectral range from 400 nm to 650 nm is, in an advantageous embodiment,at most 10%, preferably at most 8%. The reflection curve is thenrelatively flat, which is advantageous in terms of the most color-truerepresentation of the projector image possible. The percentages hereindicate the absolute difference in reflectance (based on 100% incidentlight).

The reflection spectrum for s-polarised light should also be as flat aspossible, i.e., should have no pronounced maxima and minima, inparticular in the spectral range from 450 nm to 600 nm. When thereflection spectra for both polarisation directions are sufficientlyflat, the relative proportions of s-polarised and p-polarised light canbe freely selected without this being accompanied by an undesirablecolour shift. In an advantageous embodiment, the reflectance fors-polarised light in the spectral range from 450 nm to 600 nm issubstantially constant. In the context of the invention, this means thatthe difference between the maximum reflectance occurring and the meanand the difference between the minimum reflectance occurring and themean are at most 5%, preferably at most 3%, particularly preferably atmost 1%. The percentages here indicate the absolute difference inreflectance (based on 100% incident light).

The projector is arranged on the inside of the composite pane andirradiates the composite pane via the interior-side surface of the innerpane. It is aimed at the HUD region and irradiates it to generate theHUD projection. The light of the projector has, according to theinvention, a p-polarised component >0%. In principle, the p-polarisedcomponent can even be 100%; i.e., the projector can emit purelyp-polarised light. For the overall intensity of the HUD, it is, however,advantageous for the light of the projector to have both s-polarised andp-polarised components. In this case, the p-polarised light componentsare efficiently reflected by the coating; and the s-polarised lightcomponents, by the pane surfaces. The ratio of p-polarised lightcomponents to s-polarised light components can be freely selectedaccording to the requirements of the individual case. The proportion ofp-polarised light in the total light of the projector is, for example,from 20% to 100%, preferably from 20% to 80%. In a particularlyadvantageous embodiment, the proportion of p-polarised light is at least50%, i.e., from 50% to 100%, preferably from 50% to 80%, ensuring, inparticular, that a driver with polarisation-selective sunglasses canperceive a high-intensity image. The indication of the polarisationdirection refers to the plane of incidence of the light on the compositepane. The expression “p-polarised light” refers to light whose electricfield oscillates in the plane of incidence. “S-polarised light” refersto light whose electric field oscillates perpendicular to the plane ofincidence. The plane of incidence is generated by the vector ofincidence and the surface normal of the composite pane in the geometriccentre of the HUD region.

The light of the projector preferably strikes the composite pane with anangle of incidence from 50° to 80°, in particular from 60° to 70°,typically about 65°, as is customary with HUD projection arrangements.The angle of incidence is the angle between the vector of incidence ofthe projector light and the surface normal in the geometric centre ofthe HUD region.

The electrically conductive coating according to the invention has, in apreferred embodiment, at least two functional, electrically conductivelayers, particularly preferably at least three electrically conductivelayers, most particularly preferably at least four electricallyconductive layers, in particular exactly four electrically conductivelayers. Due to the high number of conductive layers, sufficient degreesof freedom are available for optimizing the coating in terms oftransmittance and reflection behaviour and colouration.

The functional, electrically conductive layers are responsible for theelectrical conductivity of the coating. By dividing the entireconductive material into multiple layers separate from one another, thelayers can be designed thinner in each case, as a result of which thetransparency of the coating is increased. Each electrically conductivelayer preferably contains at least one metal or one metal alloy, forexample, silver, aluminium, copper, or gold, and is particularlypreferably based on the metal or the metal alloy, in other words,consists substantially of the metal or the metal alloy apart from anydopants or impurities. Preferably used is silver or a silver-containingalloy. In an advantageous embodiment, the electrically conductive layercontains at least 90 wt.-% silver, preferably at least 99 wt.-% silver,particularly preferably at least 99.9 wt.-% silver.

Each electrically conductive layer preferably has a layer thickness from3 nm to 20 nm, particularly preferably from 5 nm to 15 nm. The totallayer thickness of all electrically conductive layers is preferably from20 nm to 50 nm, particularly preferably from 30 nm to 40 nm.

According to the invention, dielectric layers or layer sequences arearranged between the electrically conductive layers and below the lowestconductive layer and above the uppermost conductive layer. Eachdielectric layer or layer sequence has at least one anti-reflectivelayer. The anti-reflective layers reduce the reflection of visible lightand thus increase the transparency of the coated pane. Theanti-reflective layers contain, for example, silicon nitride (SiN),mixed silicon-metal nitrides such as silicon-zirconium nitride (SiZrN),aluminium nitride (AlN), or tin oxide (SnO). The anti-reflective layerscan also have dopants. The layer thickness of the individualanti-reflective layers is preferably from 10 nm to 70 nm.

The anti-reflective layers can in turn be subdivided into at least twosublayers, in particular into a dielectric layer having a refractiveindex smaller than 2.1 and an optically high refractive layer having arefractive index greater than or equal to 2.1. Preferably, at least oneanti-reflective layer arranged between two electrically conductivelayers is subdivided in this way, particularly preferably eachanti-reflective layer arranged between two electrically conductivelayers. The subdivision of the anti-reflective layer results in lowersheet resistance of the electrically conductive coating with, at thesame time, high transmittance and high colour neutrality. The order ofthe two sublayers can, in principle, be selected arbitrarily, with theoptically high refractive layer preferably arranged above the dielectriclayer, which is particularly advantageous in terms of the sheetresistance. The thickness of the optically high refractive layer ispreferably from 10% to 99%, particularly preferably from 25% to 75% ofthe total thickness of the anti-reflective layer.

The optically high refractive layer having a refractive index greaterthan or equal to 2.1 contains, for example, MnO, WO₃, Nb₂O₅, Bi₂O₃,TiO₂, Zr₃N₄, and/or AlN, preferably mixed silicon-metal nitride, forexample, mixed silicon-aluminium nitride, mixed silicon-hafnium nitride,or mixed silicon-titanium nitride, particularly preferably mixedsilicon-zirconium nitride (SiZrN). This is particularly advantageous interms of the sheet resistance of the electrically conductive coating.The mixed silicon-zirconium nitride preferably has dopants. The layer ofan optically high refractive material can contain, for example, analuminium-doped mixed silicon-zirconium nitride. The zirconium contentis preferably between 15 and 45 wt.-%, particularly preferably between15 and 30 wt.-%.

The dielectric layer having a refractive index lower than 2.1 preferablyhas a refractive index n between 1.6 and 2.1, particularly preferablybetween 1.9 and 2.1. The dielectric layer preferably contains at leastone oxide, for example, tin oxide, and/or one nitride, particularlypreferably silicon nitride.

In a preferred embodiment, each anti-reflective layer arranged betweentwo electrically conductive layers is subdivided into a dielectric layerhaving a refractive index lower than 2.1 and an optically highrefractive layer having a refractive index greater than or equal to 2.1.The thickness of each antireflection arranged between two electricallyconductive layers is from 15 nm to 60 nm. The anti-reflective layersabove the uppermost electrically conductive layer and below the lowestelectrically conductive layer can also be subdivided, but are preferablyimplemented as individual layers and have, in each case, a thicknessfrom 10 nm to 25 nm.

In an advantageous embodiment, one or a plurality of dielectric layersequences has/have a first matching layer, preferably each dielectriclayer sequence that is arranged below an electrically conductive layer.The first matching layer is preferably arranged above theanti-reflective layer.

In an advantageous embodiment, one or more dielectric layer sequenceshas/have a smoothing layer, preferably each dielectric layer sequencethat is arranged between two electrically conductive layers. Thesmoothing layer is arranged below one of the first matching layers,preferably between the anti-reflective layer and the first matchinglayer. The smoothing layer preferably makes direct contact with thefirst matching layer. The smoothing layer is responsible foroptimisation, in particular smoothing of the surface for an electricallyconductive layer subsequently applied above it. An electricallyconductive layer deposited on a smoother surface has highertransmittance with, at the same time, lower sheet resistance. The layerthickness of a smoothing layer is preferably from 3 nm to 20 nm,particularly preferably from 4 nm to 12 nm. The smoothing layerpreferably has a refractive index of less than 2.2.

The smoothing layer preferably contains at least one non-crystallineoxide. The oxide can be amorphous or partially amorphous (and thuspartially crystalline) but is not completely crystalline. Thenon-crystalline smoothing layer has low roughness and thus forms anadvantageously smooth surface for the layers to be applied above thesmoothing layer. The non-crystalline smoothing layer is furtherresponsible for an improved surface structure of the layer depositeddirectly above the smoothing layer, which is preferably the firstmatching layer. The smoothing layer can contain, for example, at leastone oxide of one or more of the elements tin, silicon, titanium,zirconium, hafnium, zinc, gallium, and indium. The smoothing layerparticularly preferably contains a non-crystalline mixed oxide. Thesmoothing layer most particularly preferably contains a mixed tin-zincoxide (ZnSnO). The mixed oxide can have dopants. The smoothing layer cancontain, for example, an antimony-doped mixed tin-zinc oxide. The mixedoxide preferably has substoichiometric oxygen content. The tin contentis preferably between 10 and 40 wt.-%, particularly preferably between12 and 35 wt.-%.

In an advantageous embodiment, one or more dielectric layer sequences,preferably each dielectric layer sequence, has/have a second matchinglayer that is arranged above an electrically conductive layer. Thesecond matching layer is preferably arranged below the anti-reflectivelayer.

The first and the second matching layers are responsible for animprovement of the sheet resistance of the coating. The first matchinglayer and/or the second matching layer preferably contains zinc oxideZnO1-δ with 0<δ<0.01. The first matching layer and/or the secondmatching layer further preferably contains dopants. The first matchinglayer and/or the second matching layer can, for example, containaluminium-doped zinc oxide (ZnO:Al). The zinc oxide is preferablydeposited substoichiometrically with respect to oxygen in order to avoida reaction of excess oxygen with the silver-containing layer. The layerthicknesses of the first matching layer and the second matching layerare preferably from 3 nm to 20 nm, particularly preferably from 4 nm to12 nm.

In an advantageous embodiment, the electrically conductive coatingincludes one or more blocking layers. Preferably, at least one blockinglayer is associated with at least one, particularly preferably with eachelectrically conductive layer. The blocking layer makes direct contactwith the electrically conductive layer and is arranged immediately aboveor immediately below the electrically conductive layer. I.e., no otherlayer is arranged between the electrically conductive layer and theblocking layer. A blocking layer can also be arranged immediately aboveand immediately below a conductive layer in each case. The blockinglayer preferably contains niobium, titanium, nickel, chromium, and/oralloys thereof, particularly preferably nickel-chromium alloys. Thelayer thickness of the blocking layer is preferably from 0.1 nm to 2 nm,particularly preferably from 0.1 nm to 1 nm. A blocking layerimmediately below the electrically conductive layer serves in particularto stabilise the electrically conductive layer during a temperaturetreatment and improves the optical quality of the electricallyconductive coating. A blocking layer immediately above the electricallyconductive layer prevents contact of the sensitive electricallyconductive layer with the oxidising reactive atmosphere during thedeposition of the following layer by reactive cathodic sputtering, forexample, of the second matching layer.

In the context of the invention, if a first layer is arranged “above” asecond layer, this means that the first layer is arranged farther fromthe substrate on which the coating is applied than the second layer. Inthe context of the invention, if a first layer is arranged “below” asecond layer, this means that the second layer is arranged farther fromthe substrate than the first layer. In the context of the invention, ifa first layer is arranged “above or below” a second layer, this does notnecessarily mean that the first and the second layer are in directcontact with one another. One or more additional layers can be arrangedbetween the first and the second layer provided this is not explicitlyruled out. The values indicated for refractive indexes are measured at awavelength of 550 nm.

The electrically conductive coating with the reflection characteristicsaccording to the invention is, in principle, realisable in various ways,preferably using the above-described layers such that the invention isnot restricted to a specific layer sequence. In the following, aparticularly preferred embodiment of the coating, with whichparticularly good results are achieved, in particular with a typicalangle of incidence of the light of about 65°, is presented.

In the particularly preferred embodiment, the conductive coating has atleast four, in particular exactly four, electrically conductive layers.Each electrically conductive layer preferably has a layer thickness from3 nm to 20 nm, particularly preferably from 5 nm to 15 nm. The totallayer thickness of all electrically conductive layers is preferably from20 nm to 50 nm, particularly preferably from 30 nm to 40 nm.

The anti-reflective layer between the second and the third conductivelayer is significantly thicker (preferably from 45 nm to 55 nm) than theanti-reflective layers between the first and second conductive layer andbetween the third and fourth conductive layer (preferably from 15 nm to35 nm, with, in particular, one of the two anti-reflective layers havinga thickness from 15 nm to 25 nm; and the other, a thickness from 25 nmto 35 nm). The anti-reflective layer between the first and the secondelectrically conductive layer particularly preferably has a thicknessfrom 25 nm to 35 nm. The anti-reflective layer between the second andthe third electrically conductive layer particularly preferably has athickness from 45 nm to 55 nm. The anti-reflective layer between thethird and the fourth electrically conductive layer particularlypreferably has a thickness from 15 nm to 25 nm.

All anti-reflective layers that are arranged between two electricallyconductive layers are, as described above, subdivided into a dielectriclayer having a refractive index of less than 2.1 (preferably based onsilicon nitride) and an optically high refractive layer having arefractive index greater than or equal to 2.1 (preferably based on amixed silicon/metal nitride such as silicon-zirconium nitride orsilicon-hafnium nitride). The optically high refractive layer preferablyaccounts for from 25% to 75% of the total thickness of theanti-reflective layers.

The anti-reflective layers below the lowest conductive layer and abovethe uppermost conductive layer are implemented as single layers with alayer thickness from 10 nm to 25 nm. Preferably, the anti-reflectivelayer below the lowest conductive layer based on silicon nitride isimplemented with a thickness from 15 nm to 25 nm; and theanti-reflective layer above the uppermost conductive layer based on amixed silicon/metal nitride such as silicon-zirconium nitride orsilicon-hafnium nitride, with a thickness from 8 nm to 18 nm.

The particularly preferred embodiment of the coating also containsmatching layers and smoothing layers, as well as optional blockinglayers, as described above.

A most particularly preferred embodiment of the electrically conductivecoating contains or consists of the following layer sequence startingfrom the substrate:

-   -   an anti-reflective layer based on silicon nitride with a        thickness from 20 nm to 23 nm,    -   a first matching layer based on zinc oxide with a thickness from        8 nm to 12 nm,    -   an electrically conductive layer based on silver with a        thickness from 8 nm to 11 nm,    -   optionally, a blocking layer based on NiCr with a thickness from        0.1 nm to 0.5 nm,    -   a second matching layer based on zinc oxide with a thickness        from 8 nm to 12 nm,    -   an anti-reflective layer with a thickness from 28 nm to 32 nm,        preferably subdivided into a dielectric layer based on silicon        nitride with a thickness from 14 nm to 17 nm and an optically        high refractive layer based on a mixed silicon/metal nitride        such as silicon-zirconium nitride or silicon-hafnium nitride        with a thickness from 14 nm to 17 nm,    -   a smoothing layer based on mixed tin-zinc oxide with a thickness        from 5 nm to 9 nm,    -   a first matching layer based on zinc oxide with a thickness from        8 nm to 12 nm,    -   an electrically conductive layer based on silver with a        thickness from 11 nm to 14 nm,    -   optionally, a blocking layer based on NiCr with a thickness from        0.1 nm to 0.5 nm,    -   a second matching layer based on oxide with a thickness from 8        nm to 12 nm,    -   an anti-reflective layer with a thickness from 48 nm to 52 nm,        preferably subdivided into a dielectric layer based on silicon        nitride with a thickness from 33 nm to 37 nm and an optically        high refractive layer based on a mixed silicon/metal nitride        such as silicon-zirconium nitride or silicon-hafnium nitride        with a thickness from 14 nm to 17 nm,    -   eine smoothing layer based on mixed tin-zinc oxide with a        thickness from 5 nm to 9 nm,    -   eine first matching layer based on zinc oxide with a thickness        from 8 nm to 12 nm,    -   an electrically conductive layer based on silver with a        thickness from 8 nm to 11 nm,    -   optionally, a blocking layer based on NiCr with a thickness from        0.1 nm to 0.5 nm,    -   a second matching layer based on zinc oxide with a thickness        from 8 nm to 12 nm,    -   an anti-reflective layer with a thickness from 18 nm to 22 nm,        preferably subdivided into a dielectric layer based on silicon        nitride with a thickness from 4 nm to 7 nm and an optically high        refractive layer based on a mixed silicon/metal nitride such as        silicon-zirconium nitride or silicon-hafnium nitride with a        thickness from 14 nm to 17 nm,    -   a smoothing layer based on mixed tin-zinc oxide with a thickness        from 5 nm to 9 nm,    -   a first matching layer based on zinc oxide with a thickness from        8 nm to 12 nm,    -   an electrically conductive layer based on silver with a        thickness from 4 nm to 7 nm,    -   optionally, a blocking layer based on NiCr with a thickness from        0.1 nm to 0. nm,    -   a second matching layer based on zinc oxide with a thickness        from 8 nm to 12 nm,    -   an anti-reflective layer based on a mixed silicon/metal nitride        such as silicon-zirconium nitride or silicon-hafnium nitride        with a thickness from 11 nm to 15 nm,

When a layer is based on a material, the layer consists for the mostpart of this material in addition to any impurities or dopants.

As with other generic projection arrangements, unwanted secondary images(so-called “ghost images”), which are in particular perceived by driverswithout polarisation-selective sunglasses, can occur. The s-polarisedlight components are first reflected at the interior-side surface of theinterpane facing away from the intermediate layer. The non-reflectedpartial beam passes through the composite pane and is reflected again atthe exterior-side surface of the outer pane facing away from theintermediate layer. This generates an unwanted second virtual image, theso-called “ghost image” or “ghost”. It is advisable to take measures toprevent or at least to reduce the occurrence of the ghost image. To thisend, two embodiments are proposed in the context of the invention.

In a first advantageous embodiment, a so-called “wedge film” is used asa thermoplastic intermediate layer. The thickness of the intermediatelayer is variable over its vertical course between the lower edge andthe upper edge of the composite pane at least in the HUD region, inparticular increasing monotonically. The thickness can also vary in theentire vertical course, in particular can increase monotonicallystarting from the lower edge to the upper edge. “Vertical course” is thecourse between the lower edge and the upper edge with the direction ofthe course substantially perpendicular to said edges. The angle betweenthe two surfaces of the intermediate layer is referred to as a “wedgeangle”. If the wedge angle is not constant, the tangents to the surfaceat one point must be used for its measurement. The wedge angle ispreferably from 0.2 mrad to 1 mrad, particularly preferably from 0.3mrad to 0.7 mrad, most particularly preferably from 0.4 mrad to 0.5mrad. Due to the wedge angle of the intermediate layer, the non-parallelouter pane and inner pane enclose precisely that wedge angle. In thecase of parallel pane surfaces, the image (generated by reflection ofthe s-polarised light component at the interior-side surface of theinner pane) and the ghost image (generated by reflection of thes-polarised light component at the exterior-side surface of the outerpane) would appear offset relative to one another, which is disturbingfor the viewer. Due to the wedge angle, the ghost image is substantiallysuperimposed spatially with the image such that the viewer onlyperceives a single image or the distance between the image on the ghostimage is at least reduced.

At least in the HUD region, the intermediate layer is wedge-shaped orwedge-like, with the wedge angle suitably selected to superimpose theprojection images that are caused by the reflections at theinterior-side surface of the inner pane and at the exterior-side surfaceof the outer pane, or at least to reduce the distance between them.

The wedge angle of the intermediate layer can be constant over itsvertical course, resulting in a linear variation in thickness of theintermediate layer, with the thickness typically becoming greater fromthe bottom upward. The directional indication “from the bottom upward”refers to the direction from the lower edge to the upper edge, i.e, thevertical course. However, there can be more complex thickness profiles,in which the wedge angle is variable, linearly or non-linearly, from thebottom upward (in other words, dependent on position over its verticalcourse).

In principle, instead of a wedge film in the intermediate layer, awedge-like inner pane or outer pane can also be used to angle thereflective surfaces relative to one another.

In a second advantageous embodiment, an anti-reflective coating isapplied on the interior-side surface of the inner pane. This suppressesthe HUD image that would be generated by reflection of the interior-sidesurface of the inner pane. The (s-polarised) HUD image is generated onlyby the reflection at the exterior-side surface of the outer pane and noghost image or only a noticeably reduced intensity ghost image occurs.

The anti-reflective coating is preferably a layer sequence withalternatingly high and low refractive index which leads, due tointerference effects, to a reduction of the reflection at the coatedsurface. Such anti-reflective coatings are known per se.

The presence of the anti-reflective coating affects the reflectionbehaviour of the composite pane. The anti-reflective coating ispreferably adjusted, in particular by suitable selection of materialsand layer thicknesses such that the composite pane with the electricallyconductive coating and the anti-reflective coating satisfies therequirements according to the invention for reflection behaviour, i.e.,in particular, in the spectral range from 400 nm to 650 nm, has only asingle local reflection maximum for p-polarised light, which is in therange from 510 nm to 550 nm. The above described preferred embodimentsapply accordingly:

The anti-reflective coating can be implemented in various ways, and theinvention is not restricted to a specific layer sequence. Theanti-reflective coating preferably includes, starting from thesubstrate, a high refractive layer with a refractive index greater than1.8, above it a low refractive layer with a refractive index smallerthan 1.8, above it another high refractive layer with a refractive indexgreater than 1.8, and above it another low refractive layer with arefractive index smaller than 1.8.

In a particularly preferred embodiment, with which good results areachieved, the anti-reflective coating includes the following layersstarting from the substrate (i.e., the interior-side surface of theinner pane):

-   -   a layer (high refractive layer) based on silicon nitride,        tin-zinc oxide, silicon-zirconium nitride, or titanium oxide,        preferably silicon nitride, with a thickness from 15 nm to 25        nm, preferably from 18 nm to 22 nm,    -   a layer (low refractive layer) based on silicon dioxide with a        thickness from 15 nm to 25 nm, preferably from 18 nm to 22 nm,    -   a layer (high refractive layer) based on silicon nitride,        tin-zinc oxide, silicon-zirconium nitride, or titanium oxide,        preferably silicon nitride, with a thickness from 90 nm to 110        nm, preferably from 95 nm to 105 nm,    -   a layer (low refractive layer) based on silicon dioxide with a        thickness from 80 nm to 100 nm, preferably from 85 nm to 95 nm.

In the second advantageous embodiment as well, the intermediate layercan be wedge-shaped, for example, to superimpose the s-polarised image(from the reflection at the exterior-side surface of the outer pane) andthe p-polarised image (from the reflection at the conductive coating)and thus to reduce the occurrence of a layer ghost image for driverswithout polarisation-selective sunglasses. The intermediate layer isthen, at least in the HUD region, wedge-shaped or wedge-like, with thewedge angle suitably selected to superimpose the projection images thatare caused by the reflections at the electrically conductive coating andat the exterior-side surface of the outer pane, or at least to reducethe distance between them.

Due to the smaller distance between the reflection planes, the distancebetween the primary image and the ghost image in the case of a layerghost image is smaller than with a ghost image generated by the panesurfaces, as a result of which the layer ghost image is less disturbing.Consequently, it is possible to use an intermediate layer, whosethickness is substantially constant in the vertical course between theupper edge and the lower edge. Such a non-wedge-shaped intermediatelayer is preferred, because it is significantly more economical, asresult of which the pane can be produced more economically. Theconspicuousness of the layer ghost image is within acceptable limits inthe case of typical composite panes such that no measures need be takento avoid it.

The outer pane and the inner pane are preferably made of glass, inparticular of soda lime glass, which is customary for window panes. Inprinciple, however, the pane can also be made of other types of glass(for example, borosilicate glass, quartz glass, aluminosilicate glass)or transparent plastics (for example, polymethyl methacrylate orpolycarbonate). The thickness of the outer pane and the inner pane canvary widely. Preferably used are panes with a thickness in the rangefrom 0.8 mm to 5 mm, preferably from 1.4 mm to 2.5 mm, for example,those with the standard thicknesses of 1.6 mm or 2.1 mm.

The outer pane, the inner pane, and/or the thermoplastic intermediatelayer can be clear and colourless, but also tinted or coloured. In apreferred embodiment, the total transmittance through the windshield isgreater than 70%. The term “total transmittance” is based on the processfor testing the light permeability of motor vehicle windows specified byECE-R 43, Annex 3, § 9.1. The outer pane and the inner panes can,independently of one another, be non-prestressed, partially prestressed,or prestressed. If at least one of the panes is to be prestressed, thiscan be thermal or chemical prestressing.

The composite pane is preferably curved in one or a plurality of spatialdirections, as is customary for motor vehicle window panes, whereintypical radii of curvature are in the range from approx. 10 cm toapprox. 40 m. The composite pane can, however, also be flat, forexample, when it is intended as a pane for buses, trains, or tractors.

The thermoplastic intermediate layer contains at least a thermoplasticpolymer, preferably ethylene vinyl acetate (EVA), polyvinyl butyral(PVB), or polyurethane (PU) or mixtures or copolymers or derivativesthereof, particularly preferably PVB. The intermediate layer istypically formed from a thermoplastic film. The thickness of theintermediate layer is preferably from 0.2 mm to 2 mm, particularlypreferably from 0.3 mm to 1 mm. When a wedge-shaped layer is used, thethickness is determined at the thinnest point, typically at the loweredge of the composite pane.

The composite pane can be produced by methods known per se. The outerpane and the inner pane are laminated together via the intermediatelayer, for example, by autoclave methods, vacuum bag methods, vacuumring methods, calender methods, vacuum laminators, or combinationsthereof. The bonding of the outer pane and the inner pane is customarilydone under the action of heat, vacuum, and/or pressure.

The electrically conductive coating is preferably applied by physicalvapour deposition (PVD) onto the inner pane, particularly preferably bycathodic sputtering (“sputtering”), most particularly preferably bymagnetron-enhanced cathodic sputtering. The same applies to theanti-reflective coating, if there is one. The coating or coatings arepreferably applied on the panes before lamination. Instead of applyingthe electrically conductive coating on a pane surface, it can, inprinciple also be provided on a carrier film that is arranged in theintermediate layer.

If the composite pane is to be curved, the outer pane and the inner paneare subjected to a bending process, preferably before lamination andpreferably after any coating processes. Preferably, the outer pane andthe inner pane are bent congruently together (i.e., at the same time andby the same tool), since, thus, the shape of the panes is optimallymatched for the subsequently occurring lamination. Typical temperaturesfor glass bending processes are, for example, 500° C. to 700° C.

The invention also includes the use of a composite pane implementedaccording to the invention as a projection surface of a projectionarrangement for a head-up display, wherein a projector, whose light hasat least one p-polarised portion, is aimed at the HUD region. Theabove-described preferred embodiments apply accordingly to the use. Theprojection arrangement is preferably used as an HUD in a motor vehicle,in particular a passenger car or a truck.

In the following, the invention is explained in detail with reference todrawings and exemplary embodiments. The drawings are schematicrepresentations and are not true to scale. The drawings in no wayrestrict the invention.

They Depict:

FIG. 1 a cross-section through a composite pane as part of a genericprojection arrangement,

FIG. 2 a plan view of the composite pane of FIG. 1 ,

FIG. 3 a cross-section through a first embodiment of the composite paneaccording to the invention,

FIG. 4 a cross-section through a second embodiment of the composite paneaccording to the invention,

FIG. 5 a cross-section through an electrically conductive coatingaccording to the invention,

FIG. 6 a cross-section through an anti-reflective coating according tothe invention,

FIG. 7 reflection spectra of a composite pane with an electricallyconductive coating according to the invention and a composite pane witha prior art electrically conductive coating.

FIG. 1 depicts a generic projection arrangement for an HUD. Theprojection arrangement comprises a composite pane 10, in particular thewindshield of a passenger car. The projection arrangement also comprisesa projector 4 that is aimed at a region B of the composite pane 10. Inthe region B, usually referred to as the HUD region, the projector 4 cangenerate images that are perceived by a viewer 5 (vehicle driver) asvirtual images on the side of the composite pane 10 facing away from himif his eyes are situated within the so-called eye box E.

The composite pane 10 is constructed from an outer pane 1 and an innerpane 2 that are joined to one another via a thermoplastic intermediatelayer 3. Its lower edge U is arranged downward in the direction of theengine of the passenger car; its upper edge O upward in the direction ofthe roof. The composite pane 10 also includes an electrically conductivecoating (not shown), which is, for example, provided as an IR-reflectivecoating or as a heatable coating in. In the installed position, theouter pane 1 faces the outside environment; the inner pane 2, thevehicle interior.

The light of the projector 4 comprises a mixture of s-polarised andp-polarised components. Since the projector 4 irradiates the compositepane 10 with an angle of incidence of about 65°, which is close toBrewster's angle, the s-polarised light components are predominatelyreflected by the surfaces of the composite pane 10. The electricallyconductive coating according to the invention is, on the other hand,optimized for the reflection of the p-polarised light components. Aviewer 5 with polarisation-selective sunglasses that allow onlyp-polarised light to pass can, consequently, perceive the HUDprojection. With prior art projection arrangements that operate onlywith s-polarised light, this is not the case. A viewer 5 withoutsunglasses sees the sum of s-polarised and p-polarised light such thatthe intensity of the HUD projection is not reduced for him. These aremajor advantages of the invention.

FIG. 2 depicts a plan view of the composite pane 10 of FIG. 1 . Theupper edge O, the lower edge U, and the HUD region B are discernible.

FIG. 3 depicts a first embodiment of a composite pane 10 implementedaccording to the invention. The outer pane 1 has an exterior-sidesurface I that faces the outside environment in the installed positionand an interior-side surface II that faces the interior in the installedposition. Likewise, the inner pane 2 has an exterior-side surface IIIthat faces the outside environment in the installed position and aninterior-side surface IV that faces the interior in the installedposition. The outer pane 1 and the inner pane 2 are made, for example,of soda lime glass. The outer pane 1 has, for example, a thickness of2.1 mm; the inner pane 2, a thickness of 1.6 mm. The intermediate layer3 is made, for example, of a PVB film with a thickness of 0.76 mm

The exterior-side surface III of the inner pane 2 is provided with theelectrically conductive coating 20 according to the invention.

The s-polarised light components of the projector 4 are in each casepartially reflected at the interior-side surface of the inner pane 1(primary reflection) and the exterior-side surface of the outer pane 1(secondary reflection). No appreciable refractive index transitionoccurs at the boundary surfaces between the panes 1, 2 and theintermediate layer 3 such that they do not form any reflection surfaces.In a prior art composite pane 10 with parallel surfaces, the tworeflections result in two HUD projections offset relative to one another(a primary image and a so-called “ghost image”), which is disturbing forthe viewer 5. To avoid or to at least reduce this, the intermediatelayer 3 is wedge-shaped. The thickness of the intermediate layer 3increases continuously over its vertical course from the lower edge U tothe upper edge O. For the sake of simplicity, in the figure, theincrease in thickness is depicted linearly, but can also have morecomplex profiles. The wedge angle α describes the angle between the twosurfaces of the intermediate layer and is, for example, about 0.5 mrad.Due to the wedge-like intermediate layer, which results in an angledarrangement of the two reflection surfaces I, IV, the primary image andthe ghost image are ideally superimposed exactly, but, at least thedistance between them is reduced.

FIG. 4 depicts a further embodiment of a composite pane 10 implementedaccording to the invention. The outer pane 1 and the inner pane 2 aredesigned the same as in FIG. 3 . Here, as well, the electricallyconductive coating 20 is applied on the exterior-side surface III of theinner pane 2. Here, the intermediate layer 3 is is not wedge-shaped, buthas the form of a standard film with a constant thickness of, forexample, 0.76 mm. The ghost image problem is solved here in a differentway: the interior-side surface IV of the inner pane 2 is is providedwith an anti-reflective coating 30. This suppresses the reflection atthe surface IV such that the s-polarised light components are reflectedonly at the exterior-side surface I of the outer pane. Theanti-reflective coating 30 according to the invention is adjusted suchthat it does not substantially shift the reflection spectrum of thecomposite pane 10 for p-polarised light such that the propertiesaccording to the invention with regard to p-polarised light are stillretained.

In both embodiments, a viewer 5 without polarisation-selectivesunglasses will perceive, in addition to the HUD projection generated atthe exterior-side surface I (s-polarised), a so-called “layer ghostimage” (p-polarised) that is generated by the electrically conductivecoating 20. The distance between the two reflection planes issufficiently small with customary pane thicknesses for the layer ghostimage to be within acceptable limits. The distance between the twoprojections could be reduced even further if the electrically conductivecoating 20 were applied on the interior-side surface of the outer paneII and/or a thinner outer pane 1 and/or a thinner intermediate layer 3were used.

FIG. 5 depicts the layer thickness of an electrically conductive coating20 according to the invention. The coating 20 contains four electricallyconductive layers 21 (21.1, 21.2, 21.3, 21.4). Each electricallyconductive layer 21 is in each case arranged between two of a total offive anti-reflective layers 22 (22.1, 22.2, 22.3, 22.4, 22.5). Theanti-reflective layers 22.2, 22.3, 22.4 that are arranged between twoelectrically conductive layers 21, are in each case subdivided into adielectric layer 22 a (22 a.2, 22 a.3, 22 a.4) and an optically highrefractive layer 22 b (22 b.2, 22 b.3, 22 b.4). The coating 20 alsocontains three smoothing layers 23 (23.2, 23.3, 23.4), four firstmatching layers 24 (24.1, 24.2, 24.3, 24.4), four second matching layers25 (25.2, 25.3, 25.4, 25.5), and for blocking layers 26 (26.1, 26.2,26.3, 26.4).

The layer sequence can be seen schematically in the figure. The layersequence of a composite pane 10 with the coating 20 on the exterior-sidesurface III of the inner pane 2 is also presented, together with thematerials and layer thicknesses of the individual layers, in Table 1(Example). Table 1 also depicts the layer sequence of an electricallyconductive coating, as it is currently already in use (ComparativeExample). It can be seen that the reflection properties of the coating20 according to the invention were achieved by suitable optimisation ofthe layer thicknesses of the individual layers.

FIG. 6 depicts the layer sequence of an anti-reflective coating 30 inthe context of the invention, comprising two high refractive layers 31(31.1, 31.2) and two low refractive layers 32 (32.1, 32.2). The layersequence can be seen schematically in the figure. The layer sequence ofa composite pane 10 with the electrically conductive coating 20 on theexterior-side surface III of the inner pane 2 and the anti-reflectivecoating 30 on the interior-side surface IV of the inner pane 2 is alsoshown in Table 2, together with the materials and layer thicknesses ofthe individual layers.

TABLE 1 Layer Thickness Material Reference Character Example ComparativeExample Glass 1 2.1 mm 2.1 mm PVB 3 0.76 mm 0.76 mm SiZrN 20 22.5 12.3nm 25.2 nm ZnO 25.5 10.0 nm 10.0 nm NiCr 26.4 0.2 nm 0.2 nm Ag 21.4 5.3nm 14.1 nm ZnO 24.4 10.0 nm 10.0 nm SnZnO:Sb 23.4 7.0 nm 7.0 nm SiZrN22b.4 22.4 15.0 22.9 nm SiN 22a.4 5.2 nm 29.8 nm ZnO 25.4 10.0 nm 10.0nm NiCr 26.3 0.2 nm 0.2 nm Ag 21.3 9.6 nm 14.2 nm ZnO 24.3 10.0 nm 10.0nm SnZnO:Sb 23.3 7.0 nm 7.0 nm SiZrN 22b.3 22.3 15.0 nm 20.1 nm SiN22a.3 35.1 nm 29.6 nm ZnO 25.3 10.0 nm 10.0 nm NiCr 26.2 0.2 nm 0.2 nmAg 21.2 12.4 nm 17.1 nm ZnO 24.2 10.0 nm 10.0 nm SnZnO:Sb 23.2 7.0 nm7.0 nm SiZrN 22b.2 22.2 15.0 nm 19.4 nm SiN 22a.2 15.5 nm 34.1 nm ZnO25.2 10.0 nm 10.0 nm NiCr 26.1 0.2 nm 0.2 nm Ag 21.1 9.5 nm 11.7 nm ZnO24.1 10.0 nm 10.0 nm SiN 22.1 21.2 nm 28.8 nm Glass 2 1.6 mm 1.6 nm

TABLE 2 Material Reference Character Layer Thickness SiO 30 32.2 92.7 nmSiN 31.2 102.2 nm SiO 32.1 20.5 nm SiN 31.1 19.9 nm Glass 2 1.6 mm 20 (See Table 1) PVB 3 0.76 mm Glass 1 2.1 mm

FIG. 7 depicts the reflection spectrum of a composite pane 10 with aprior art conductive coating 20 per the Comparative Example and aconductive coating 20 according to the invention per the Example (cf.Table 1) for p-polarised light (Part a) and for s-polarised light (Partb). The spectra were measured on the interior-side at an angle ofincidence of 65°, thus simulating the reflection behaviour for the HUDprojector.

The prior art coating per the Comparative Example, as it has been usedto date, has, in the spectral range from 400 nm to 650 nm forp-polarised light, two local reflection maxima: at 476 nm and at 600 nm.The difference between the reflectance of the local reflection maximumand the minimally occurring reflectance for p-polarised light in thespectral range from 400 nm to 650 nm is significantly more than 10%.

In contrast, the coating according to the invention per the Example has,in the spectral range from 400 nm to 650 nm for p-polarised light, onlya single local reflection maximum. The local reflection maximum issituated at 516 nm, i.e., in the green spectral range, for which thehuman eye is particularly sensitive. The difference between thereflectance of the local reflection maximum and the minimally occurringreflectance for p-polarised light in the spectral range from 400 nm to650 nm is only 6.7%.

For s-polarised light as well, the reflection spectrum of the coatingaccording to the invention is significantly flatter than that of theprior art coating in the spectral range from 450 nm to 600 nm. Thedifference between the maximally occurring reflectance and the mean is0.4%; the difference between the minimally occurring reflectance and themean is 0.3%.

By means of the embodiment of the coating according to the invention ofthe Example, an HUD image with neutral coloration is generated. Inaddition, the relative proportions of s-polarised and p-polarised lightcan be freely selected without being associated with a color shift orother undesirable effects. The light components are thus adjustableaccording to the requirements of the individual case, without imposinglimits on the person skilled in the art due to the coating. A ratio canbe set such that optimum intensity of the HUD projection is achieved fordrivers with and without polarisation-selective sunglasses.

Table 3 presents the total reflectance with various polarisationproportions of the projector light, on the one hand, for a prior artcomposite pane (coating 20 as specified in Table 1 under ComparativeExample, no anti-reflective coating 30), on the other, for a compositepane according to the invention (coating 20 as specified in Table 1under Example, structure with anti-reflective coating 30 as specified inTable 2). It is clear to see that the reflectance for p-polarised light(perceived by a viewer with polarisation-selective sunglasses) issignificantly increased at any polarisation ratio. The reflectance fors- and p-polarised light (perceived by a viewer withoutpolarisation-selective sunglasses) is also increased starting at ap-polarisation proportion of 50%. Overall, a more intense image results.

TABLE 3 Total reflectance/% Light Components of the ProjectorComparative Light Example Example p s s + p p s + p p 0 100 33.1 0 26.40.0 10 90 30.5 0.7 25.4 1.6 20 80 27.9 1.4 24.4 3.3 30 70 25.3 2.1 23.44.9 40 60 22.7 2.8 22.4 6.6 50 50 20.1 3.5 21.4 8.2 60 40 17.4 4.2 20.49.8 70 30 14.8 4.9 19.4 11.5 80 20 12.2 5.6 18.4 13.1 90 10 9.6 6.3 17.414.8 100 0 7.0 7.0 16.4 16.4

LIST OF REFERENCE CHARACTERS

-   (10) composite pane-   (1) outer pane-   (2) inner pane-   (3) thermoplastic intermediate layer-   (4) projector-   (5) viewer/vehicle driver-   (20) electrically conductive coating-   (21) electrically conductive layer-   (21.1), (21.2), (21.3), (21.4) 1., 2., 3., 4. electrically    conductive layer-   (22) anti-reflective layer-   (22.1), (22.2), (22.3), (22.4), (22.5) 1., 2., 3., 4., 5.    anti-reflective layer-   (22 a) dielectric layer of the anti-reflective layer 4-   (22 a.2), (22 a.3), (22 a.4) 1., 2., 3. dielectric layer-   (22 b) optically high refractive layer of the anti-reflective layer    4-   (22 b.2), (22 b.3), (22 b.4) 1., 2., 3. optically high refractive    layer-   (23) smoothing layer-   (23.2), (23.3), (23.4) 1., 2., 3. smoothing layer-   (24) first matching layer-   (24.1), (24.2), (24.3), (24.4) 1., 2., 3., 4. first matching layer-   (25) second matching layer-   (25.2), (25.3), (25.4), (25.5) 1., 2., 3., 4. second matching layer-   (26) blocking layer-   (26.1), (26.2), (26.3), (26.4) 1., 2., 3., 4. blocking layer-   (30) anti-reflective coating-   (31) high refractive layer of the anti-reflective coating 30-   (31.1), (31.2) 1., 2. high refractive layer-   (32) low refractive layer of the anti-reflective coating 30-   (32.1), (32.2) 1., 2. low refractive layer-   (O) upper edge of the composite pane 10-   (U) lower edge of the composite pane 10-   (B) HUD region of the composite pane 10-   (E) eye box-   (I) exterior-side surface of the outer pane 1, facing away from the    intermediate layer 3,-   (II) interior-side surface of the outer pane 1, facing the    intermediate layer 3,-   (III) exterior-side surface of the inner pane 2, facing the    intermediate layer 3,-   (IV) interior-side surface of the inner pane 2, facing away from the    intermediate layer 3-   α wedge angle

The invention claimed is:
 1. A projection arrangement for a head-updisplay (HUD), comprising: a composite pane, comprising an outer paneand an inner pane, which are joined to one another via a thermoplasticintermediate layer, having an upper edge and a lower edge and an HUDregion; an electrically conductive coating on a surface of the outerpane or the inner pane facing the intermediate layer or within theintermediate layer; and a projector that is aimed at the HUD region;wherein light of the projector has at least one p-polarised portion,wherein the proportion of p-polarised light in the total light of theprojector is from 20% to 80%, wherein the electrically conductivecoating has, in the spectral range from 400 nm to 650 nm, only a singlelocal reflection maximum for p-polarised light, with said single localreflection maximum situated in the range from 510 nm to 550 nm, whereinthe electrically conductive coating includes at least four electricallyconductive layers, which are in each case arranged between twodielectric layers or layer sequences, wherein each dielectric layersequence includes an anti-reflective layer, and wherein theanti-reflective layer below the first electrically conductive layer hasa thickness from 15 nm to 25 nm, the anti-reflective layer between thefirst and the second electrically conductive layer has a thickness from25 to 35 nm, the anti-reflective layer between the second and the thirdelectrically conductive layer has a thickness from 45 nm to 55 nm, theanti-reflective layer between the third and the fourth electricallyconductive layer has a thickness from 15 nm to 25 nm, and theanti-reflective layer above the fourth electrically conductive layer hasa thickness from 8 nm to 18 nm.
 2. The projection arrangement accordingto claim 1, wherein in the spectral range from 400 nm to 650 nm, adifference between the reflectance of the local reflection maximum and aminimally occurring reflectance for p-polarised light is at most 10%. 3.The projection arrangement according to claim 1, wherein the reflectancefor s-polarised light in the spectral range from 450 nm to 600 nm issubstantially constant such that a difference between the maximallyoccurring reflectance and a mean as well as a difference between theminimally occurring reflectance and the mean are at most 5%.
 4. Theprojection arrangement according to claim 1, wherein the proportion ofp-polarised light in the total light of the projector is from 50% to80%.
 5. The projection arrangement according to claim 1, wherein theelectrically conductive layers are based on silver and have, in eachcase, a layer thickness from 5 to 15 nm, wherein a total layer thicknessof all electrically conductive layers is from 20 nm to 50 nm.
 6. Theprojection arrangement according to claim 1, wherein all anti-reflectivelayers that are arranged between two electrically conductive layers aredivided into a dielectric layer having a refractive index smaller than2.1, and an optically high refractive layer having a refractive indexgreater than or equal to 2.1.
 7. The projection arrangement according toclaim 1, wherein a thickness of the intermediate layer is variable witha wedge angle in its vertical course between the upper edge and thelower edge at least in the HUD region.
 8. The projection arrangementaccording to claim 1, wherein an anti-reflective coating is applied onthe surface of the inner pane facing away from the intermediate layer.9. The projection arrangement according to claim 8, wherein a thicknessof the intermediate layer is substantially constant in the verticalcourse between the upper edge and the lower edge.
 10. The projectionarrangement according to claim 8, wherein the thickness of theintermediate layer is variable with a wedge angle in its vertical coursebetween the upper edge and the lower edge at least in the HUD region.11. The projection arrangement according to claim 1, wherein the lightof the projector strikes the composite pane with an angle of incidencefrom 60° to 70°.
 12. The projection arrangement according to claim 2,wherein the difference between the reflectance of the local reflectionmaximum and the minimally occurring reflectance for p-polarised light isat most 8%.
 13. The projection arrangement according to claim 3, whereinthe difference between the maximally occurring reflectance and the meanas well as the difference between the minimally occurring reflectanceand the mean are at most 1%.
 14. The projection arrangement according toclaim 6, wherein the dielectric layer is based on silicon nitride andthe optically high refractive layer is based on a mixed silicon/metalnitride.
 15. The projection arrangement according to claim 14, whereinthe optically high refractive layer is layer of silicon-zirconiumnitride or silicon-hafnium nitride.
 16. The projection arrangementaccording to claim 7, wherein the wedge angle is selected forsuperimposing the reflections at the interior-side surface of the innerpane and at the exterior-side surface of the outer pane or for at leastreducing the distance between them.
 17. The projection arrangementaccording to claim 10, wherein the wedge angle is selected forsuperimposing the reflections at the electrically conductive coating andat the exterior-side surface of the outer pane or for at least reducingthe distance between them.
 18. A projection arrangement for a head-updisplay (HUD), comprising: a composite pane, comprising an outer paneand an inner pane, which are joined to one another via a thermoplasticintermediate layer, having an upper edge and a lower edge and an HUDregion; an electrically conductive coating on a surface of the outerpane or the inner pane facing the intermediate layer or within theintermediate layer; and a projector that is aimed at the HUD region;wherein light of the projector has at least one p-polarised portion,wherein the proportion of p-polarised light in the total light of theprojector is from 20% to 80%, and wherein the electrically conductivecoating has, in the spectral range from 400 nm to 650 nm, only a singlelocal reflection maximum for p-polarised light, with said single localreflection maximum situated in the range from 510 nm to 550 nm, whereinan anti-reflective coating is applied on the surface of the inner panefacing away from the intermediate layer, and wherein the anti-reflectivecoating includes the following layers, starting from the inner pane: ahigh refractive layer based on silicon nitride with a thickness from 15nm to 25 nm, a low refractive layer based on silicon dioxide with athickness from 15 nm to 25 nm, a high refractive layer based on siliconnitride with a thickness from 90 nm to 110 nm, a low refractive layerbased on silicon dioxide with a thickness from 80 nm to 100 nm.
 19. Theprojection arrangement according to claim 18, wherein the electricallyconductive coating includes at least four electrically conductivelayers, which are in each case arranged between two dielectric layers orlayer sequences.
 20. A method comprising utilizing a composite pane,comprising an outer pane and an inner pane, which are joined to oneanother via a thermoplastic intermediate layer, having an upper edge anda lower edge and an HUD region and having an electrically conductivecoating on a surface of the outer pane or the inner pane facing theintermediate layer or provided within the intermediate layer, as aprojection surface of a projection arrangement for a head-up display(HUD), wherein a projector is aimed at the HUD region, whose light hasat least one p-polarised portion, wherein the proportion of p-polarisedlight in the total light of the projector is from 20% to 80%, andwherein the electrically conductive coating has, in the spectral rangefrom 400 nm to 650 nm, only a single local reflection maximum forp-polarised light, with said single local reflection maximum situated inthe range from 510 nm to 550 nm, wherein the electrically conductivecoating includes at least four electrically conductive layers, which arein each case arranged between two dielectric layers or layer sequences,wherein each dielectric layer sequence includes an anti-reflectivelayer, and wherein the anti-reflective layer below the firstelectrically conductive layer has a thickness from 15 nm to 25 nm, theanti-reflective layer between the first and the second electricallyconductive layer has a thickness from 25 to 35 nm, the anti-reflectivelayer between the second and the third electrically conductive layer hasa thickness from 45 nm to 55 nm, the anti-reflective layer between thethird and the fourth electrically conductive layer has a thickness from15 nm to 25 nm, and the anti-reflective layer above the fourthelectrically conductive layer has a thickness from 8 nm to 18 nm.